In the fields of hydrocarbon and chemical processing, contaminants such as ammonia and amines, hydrogen sulfide, carbonate, other sulfur acids and organic acids can cause a variety of problems. For example, these contaminants can lead to corrosion and fouling of equipment, and an increase in toxic emissions.
Ammonia and amines are one example of a problematic contaminant. Ammonia and amines are formed from any nitrogen present in the crude, oil, or gas to be processed as well as nitrogen bearing compounds which may be introduced during the hydrocarbon and chemical processes. When ammonia is present in a steam system, it can lead to corrosion, particularly with copper metallurgy. Ammonia may also combine with chloride or carbonate to form solids which can plug flow lines and machinery.
Ammonia is produced in the refinery primarily in three processes, namely, hydrotreating, thermal cracking units and catalytic cracking units. In all processes, ammonia may be removed from the process gas by scrubbing with wash water. This wash water is often recycled into the hydrocarbon process where ammonia may cause additional corrosion, fouling and lead to NOx emission.
Removal of contaminants such as ammonia and hydrogen sulfide using generally accepted technology has required several steps and unit operations to achieve. Presently, application of contaminant removal unit operation has been limited due to capital and operational costs. Development of a simplified and economical method to remove these contaminants has not been achieved in the art.
Reverse osmosis (RO) technology has been used to treat water systems, typically for drinking water. U.S. Pat. No. 5,925,225 to Mukhopadhyay provides a method of treating water by raising the pH above 8.5 and passing it through a nanofiltration or reverse osmosis membrane. However, Mukhopadhyay does not treat water exposed to hydrocarbon or chemical processing which may include a greater concentration of contaminants, nor does Mukhopadhyay provide a method for the removal of ammonia.
U.S. Pat. No. 4,574,049 to Pittner also provides a water purification process that may include a reverse osmosis (RO) process. Pittner mainly addresses the use of RO membranes to remove carbon dioxide. Pittner accomplishes this by first raising the pH of the water feed to convert carbon dioxide to bicarbonate or preferably carbonate to increase the concentration that will be directed as reject. However, Pittner's method is similarly deficient as Mukhopadhyay's method in failing to address the additional concerns associated with hydrocarbon and chemical process waters, including failure to address the removal of ammonia.
Therefore, a need exists for a method of contaminant removal for process water which has been exposed to hydrocarbon and chemical processing. Desirably, this process will incorporate reverse osmosis technology and will be simplified, economical, and will accomplish removal of the contaminants present in this process water. More desirably, the result will be the reduction in corrosion and fouling of equipment and reduction in toxic emissions, especially when the processed water is recycled within the hydrocarbon process.